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HISTORY OF ENZYMES
In 1833, French chemist Anselme Payen
discovered the first enzyme, diastase
...



Characters Of Enzymes
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Catalysts for biological reactions
All are globuar proteins
Lower the activation energy
Accelerate the rate of reaction
Activity lost if denatured
Very specific in aciton
May contain cofactors such as metal ions
or organic (vitamins)

Mechanism of Enzyme Action
(Catalysis)





Chemical reactions need an initial input of energy =
THE ACTIVATION ENERGY
During this part of the reaction the molecules are said
to be in a transition state
...

Enzymes can increase the rate of reactions
without increasing the temperature
...

They create a new reaction pathway “a short
cut”

The Substrate
The substrate of an enzyme are the reactants
that are activated by the enzyme
 Enzymes are specific to their substrates
 The specificity is determined by the active
site


© 2007 Paul Billiet ODWS

The Lock and Key Hypothesis
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Emil Fischer (1890) proposed this model
One specific key can open only a specific lock
A specific enzyme can transform only one substrate
into products
Fit between the substrate and the active site of the
enzyme is exact
Like a key fits into a lock very precisely
The key is analogous to the enzyme and the substrate
analogous to the lock
...
g vitamins)
...
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The effect of pH
2
...
5H

Enzyme
activity

Trypsin

Pepsin
1

3

5

7
pH

9

11

Temperature and Enzyme Activity
Enzymes are most active at an optimum
temperature (optimum temperature of enzymes of
human body is 37°C)
 Heat provide activation energy, chemical reaction
accelerated at high temperature
 Further increase in heat energy increases the
vibrations of atoms
 And globular structure essential for enzyme
activity may lost and enzyme is said to be
denatured


Temperature coefficient
 Q10

(the temperature coefficient) = the
increase in reaction rate with a 10°C rise
in temperature
...


The effect of temperature
Normal curve

Q10

Enzyme
activity

Denaturation

Optimum temperature

0

10

20
30
40
Temperature / °C

50

Inhibitors
An inhibitor is a chemical
substance which can react (in
place of substrate) with the
enzyme but is not transformed
into products and thus blocks
the active site temporarily or
permanently
...

• They occupy the active sites by
forming covalent bonds or they
may physically block the active
sites
...
Have two types

Competitive
Have
structure
similarity with the
substrate
May be selected by
the binding sites
but are not able to
activate
the
catalytic sites

Non-Competitive
They form enzyme
enzyme
inhibitor
complex at a point
other than active
site
Alter
the
structure of the
enzyme

The effect of enzyme
inhibition
Fumarate + 2H++ 2e-

Succinate
Succinate dehydrogenase

CH2COOH

COOH

CHCOOH

CH2
CH2COOH

COOH
Malonate

CHCOOH



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